Lecture 9: Fermentation and Wine Making

Question 1

What is the history of microbial biotechnology?

Answer 1

Earliest known wine production: 6000 BCE in Georgia
Earliest known cheese making: 5200 BCE croatia

Change in pH or production of ethanol lead to inhibition of microbial growth -> preservation

Question 2

What is fermentation?

Answer 2

Definition: “an ATP-generating process where organic compounds act as both electron donors and acceptors”

Discovered by Louis Pasteur, who demonstrated that yeast was responsible for fermentation of sugar to produce alcohol

Also used to describe growth of microorganisms on or in a growth medium

Question 3

What is glycolysis?

Answer 3

First stage in aerobic respiration

Metabolises one molecule of glucose to two molecules of pyruvate, producing 2x ATP

Ancient anaerobic pathway which evolved before accumulation of substantial atmospheric O2

Exhibits feedback inhibition

Question 4

What is the TCA cycle?

Answer 4

results in the complete oxidation of glucose derivatives to CO2

Linked to glycolysis via pyruvate dehydrogenase

Pyruvate + CoA + NAD+ = acetyle-CoA + CO2 + NADH + H+

Question 5

What is Oxidative phosphorylation?

Answer 5

Part of aerobic respiration.

TCA cycle produces NADH and oxidative phosphorylation consumes NADH

Electron transport along chain of carriers (proton gradient)

ATP synthase dissipates the proton gradient, producing ATP

Oxygen accepts electrons producing water

Question 6

How does fermentation produce ATP?

Answer 6

Via glycolysis only.

They regenerate oxidised NAD+ for glycolysis. Net ATP is thus only 2x

Question 7

What is the start and end of various organic compounds?

Answer 7

glucose > lactate
lactate > acetate
glucose > ethanol
ethanol > acetate
etc etc

Question 8

What are yeasts?

Answer 8

Eukaryotic
Kingdom: fungi
~1,500 species
Unicellular
Reproduce via budding or binary fusion

Question 9

What is Saccharomyces cerevisiae

Answer 9

‘Bakers / brewers / budding yeast’

Question 10

What is the Crabtree effect?

Answer 10

yeast being able to ferment in the present of oxygen WHEN glucose concentrations are high

This makes yeast a “facultative anaerobe”

Question 11

How did the Crabtree effect evolve?

Answer 11

~100 mya S. cerevisiae underwent whole-genome duplication (WGD). n = 8 to n = 16.

Occurred at time of diversification and proliferation of flowering plants

Fruits become more abundant

WGD lineages have pronounced Crabtree effect

Question 12

What is Malolactic fermentation?

Answer 12

Winemaking has two fermentations:
1. Alcoholic fermentation
2. Malolactic fermentation (MLF)

MLF is performed by lactic acid bacteria. It converts malic acid to lactic acid and CO2-

Essential for nearly all red wines and some white

MLF reduces total acidity

Malic acid = more tart tasting. Lactic acid = more softer tasting

Question 13

What is wine

Answer 13

Non-distilled, made from grapes or other fruits

Fruit undergoes fermentation and ageing

Alcohol: 5-13%
Contains nutrients
70-90kcal per 100ml

Question 14

What are the main steps of white wine production?

Answer 14

1. grape harvest
2. crush to release juice
3. primary fermentation
   a. white wine requires skin removal
   b. yeast added or natural yeasts used
4. Wine collected and bottled

Question 15

What are the main steps of red wine production?

Answer 15

1. grape harvest
2. crush to release juice
3. primary fermentation
4. ‘free run wine’
5. free run wine collected
6. skins and remain solids pressed
7. ‘Press wine’
8. Free run and press wines may be combined
9. Malolactic conversion. Malic acid converted to lactic acid
10. Maturation in oak barrels

Question 16

What are wine yeasts?

Answer 16

Many different genera and species found in grape ‘must’, including both Saccharomyces and non-Saccharomyces spp.

In the past, must fermentation happened by chance, often resulting in wine being:
unreliable in its production
undrinkable
vinegar

Modern wine uses cultured and selected strains

Question 17

What is noble rot?

Answer 17

caused by filamentous fungus Botrytis cinerea, causing dehydration of infected grape

This process concentrates sugars, giving sweeter flavour.

Also produces phenylacetaldehyde, giing the fruity aroma to wine

Question 18

What is noble rot?

Answer 18

caused by filamentous fungus Botrytis cinerea, causing dehydration of infected grape

This process concentrates sugars, giving sweeter flavour.

Also produces phenylacetaldehyde, giving the fruity aroma to wine

Question 19

What is sparkling wine?

Answer 19

1. Bottle filled with fermented grape must
2. Add solution of: Sucrose, selected yeasts, grape must
3. Proportions important for right CO2 pressure
4. Bentonite and sulphur dioxide added to prevent spoilage and harmful effects of oxygen
5. Bottles left somewhere cool and dry and secondary fermentation take place to produce CO2-